I. Field of the Invention
The present invention relates generally to electric field sensors.
II. Description of Related Art
There have been previously known electric field sensors used to detect the strength of a varying electric field. These electric field sensors are used in many different applications where monitoring of the E- or B-field is required.
For example, such E-field sensors may be used in the detection and trajectory measurement of charged particles. Such charged particles may be created, for example, during the firing of bullets or other armory, particle accelerators, and even dust.
Similarly, such electric field sensors may be used to measure signals passing on unshielded communication interfaces and electric buses. As such, these previously known electric field sensors may be used for communication snooping.
Electric field sensors are also used in power line sensing applications. For example, such applications include the detection of energized wires, wire localization, automatic emergency wire avoidance, as well as line following or navigation.
Still other applications for electric field sensors include weather monitoring such as lightning detection and charged thundercloud detection. Such weather applications not only facilitate weather prediction, but also form an alarm signal of dangerous weather conditions.
Electric field sensors are also used for the detection of potential hazardous conditions in industries where a spark-induced explosion may cause substantial damage. For example, petroleum refineries, paper mills, textile mills, plastic fabrication, microelectronic fabrication, and other industrial applications are all subject to spark-induced explosions or sensitive damage from electrostatic discharge (ESD) which may result from a high E-field. Furthermore, electrostatic forces caused by high E-fields, or the lack of such forces, can result in unwanted movement or deformations during the precision manufacturing fabrication.
There have been previously known electric field sensors. However, these previously known electric field sensors all suffer from a number of common disadvantages.
First, the previously known electric field sensors are primarily single axis sensors which measure the electric field, or the time derivative of the electric field, only along a single axis. In order to obtain three-dimensional measurements of the electric field, it is necessary to physically reposition the electric field sensor along a different axis and then repeat the measurements of the electric field.
A still further disadvantage of the previously known electric field sensors is that many such electric field sensors require an earth ground in order to obtain the electric field measurement. In many situations, however, it is inconvenient, or even impossible, to obtain an earth ground for the sensor.
A still further disadvantage of the previously known electric field sensors is that such sensors provide only a small output signal, e.g. a few microvolts, as the output signal from the sensor representative of the strength or time derivative of the electric field. Such small output signals are inherently subject to error due to the difficulty of instrumentation required to measure the small output signals.